tap(4): half-duplex and zero-speed ?

[Alexandre Snarskii]

Hi!

Long story short: if you try to aggregate tap(4) devices into lacp-based
lagg(4), aggregate will fail to negotiate lacp with remote end and will not 
be able to pass traffic.

Root cause: lacp code requires underlying interface to be full-duplex 
(else it will not participate in lacp negotiation at all[1]) and have 
non-zero speed (else it can not be selected as active aggregator[2],
and so if tap is the only lagg member - aggregate will not become active).

Patch can be as trivial as:

--- sys/net/if_tap.c.orig	2017-02-21 21:02:04.460053000 +0300
+++ sys/net/if_tap.c	2017-02-21 21:02:12.580696000 +0300
@@ -617,7 +617,7 @@
 			dummy = ifmr->ifm_count;
 			ifmr->ifm_count = 1;
 			ifmr->ifm_status = IFM_AVALID;
-			ifmr->ifm_active = IFM_ETHER;
+			ifmr->ifm_active = IFM_ETHER | IFM_1000_T | IFM_FDX;
 			if (tp->tap_flags & TAP_OPEN)
 				ifmr->ifm_status |= IFM_ACTIVE;
 			ifmr->ifm_current = ifmr->ifm_active;


[1]: https://svnweb.freebsd.org/base/head/sys/net/ieee8023ad_lacp.c?revision=312678&view=markup#l483
[2]: https://svnweb.freebsd.org/base/head/sys/net/ieee8023ad_lacp.c?revision=312678&view=markup#l983